Hot Standby PAC, Local Rack BMENOS0300 Topologies
Original instructions
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Hot Standby DIO Ring
In this Hot Standby topology, two BMENOS0300 network option switches are used in place of BMENOC0301/11 modules to reduce cost. The network ports of two BMENOS0300 network option switch modules – one in the primary and one in the standby – are configured for a HSBY/DIO. 
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Primary Hot Standby PAC 
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Standby Hot Standby PAC 
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Distributed equipment 
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ConneXium dual ring Ethernet managed switches 
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SCADA server 
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Engineering workstation with dual network interface cards 
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Ethernet DIO ring 
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Hot Standby communication link 
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Ethernet control network 
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BMENOC0301/11 communication module with backplane port disabled
NOTE:
  • In this design, confirm that the backplane port of each BMENOC0301/11 communication module is disabled. The backplane port is disabled by default.
    CAUTION
    RISK OF BROADCAST STORM
    Do not enable the Ethernet backplane ports of the primary and standby BMENOC0301/11 communication modules. Enabling these ports can result in the occurrence of a broadcast storm, which can prevent the Hot Standby network from transporting intended network communications.
    Failure to follow these instructions can result in injury or equipment damage.
  • To achieve acceptable recovery times, limit each DIO design to a single DIO main ring without sub-rings.
  • RSTP limits the size of the DIO ring to a maximum of 40 switched devices, including the two BMENOS0300 modules.
  • When you set the BMENOS0300 network rotary switch to HSBY/DIO, assign RSTP bridge identifier priority values greater than 4096 (decimal) to other distributed equipment Ethernet devices in the DIO ring. Refer to the topic Device Rotary Switch Positions for information about the effects of selecting HSBY/DIO.